IB 201: LABORATORY SESSION 13: ANIMAL DIVERSITYGoals: Introduce students to the diversity of animal. Relate aspects of the biology ofvarious animal phyla to their evolutionary relationships. Consider the variation withinand among animal and use the variation to address the issue of constraints in evolution.Assignment.1) Identify the live specimens in the lab to phylum and provide visible characteristics foreach.2) Map animal structure onto a phylogeny.3) Write a short assignment that relates the diversity of animal structure and biology toconstraints in evolution. What does it mean to say that evolution is constrained?IntroductionThree labs ago we did a survey of the major evolutionary groups of plants. This week wewill repeat the process for another major group of multi-cellular organisms – the animals.We have no animal equivalent of the greenhouse so we will be using living and preservedspecimens in the lab.Animals are by far the most diverse group of living organisms in terms of describedspecies with well over one million species that have been named by scientists. Animaldiversity is very well known relative to most other groups of organisms. There are tworeasons for this. Human beings are animals and it is natural that we have taken more ofan interest in the organisms that are most similar to ourselves. Also, and of morerelevance to the study of animal evolution, animals have a much greater diversity of bodyform than any other group of organisms. For centuries biologists have been studying thedetails of development and composition of animal bodies in an attempt to work out theevolutionary relationships among different animal phyla (a phylum is a major group ofanimals such the arthropoda or the mollusca). The study of the evolution of animal bodyform has led to debates about the nature of evolution itself.Specifically there has been considerable controversy about the role of animal body plansin constraining evolution. Virtually all animal phyla with substantial fossil records firstappear very early in the history of animals. Some evolutionary biologists haveinterpreted this pattern as evidence that, once basic body plans were established, itbecame very difficult, if not impossible, to evolve a new body plan from pre-existingbody plan. In other words, evolution was constrained so that animals could evolvevariations on a theme but not develop an entirely new forms. Other biologists have notbeen convinced by this argument. They argue that there is no direct evidence forconstraints and that experimental studies of evolution do not support the idea that bodyplans cannot be changed by the appropriate selective pressure.In the following two sections we review some of the terminology used in describinganimal structure and an over-view of some of the more important animal phyla. Studentswho are also in IB 202 should find some this material familiar although the context inwhich it is presented is somewhat different.TerminologyBilateral vs. Radial Symmetry – Unlike plants most animal bodies have well-definedoverall shape. Most animals are bilaterally symmetrical – the body has a single planewhich divides the body into two equal halves. Think of the human body. It can bedivided into equal left and right halves but not equal top and bottom halves or back andfront halves. Some animals such jellyfish or starfish have radial symmetry in which thebody can be divided into equal halves in multiple planes. For an analogy, think of a pieor a cake – they can be cut in half many different ways. A few animals, such as manysponges, are asymmetrical – there is no plane that can divide them in two. Radial Symmetry Bilaterial SymmetryCoelom – The coelom is the body cavity, the space in which many of the organs arefound. A typical animal can be thought of as a hollow tube containing the various organsystems. The digestive system then forms a tube within the coelom (tube inside a tubebody form). Some animals lack coeloms (they are acoelomate). Among animals withcoleoms there is variation is how the coelom is formed (see below).Blastopore – During the develop of animal embryos the zygote undergoes mitosis manytimes to form a ball of cells (blastula). The blastula then undergoes a process known asgastrulation. During gastrulation a pocket forms in the blastula, which leads to theformation of a hollow ball of cells with an opening. This opening is called a blastopore,the ball of cells is called the gastrula. The empty space inside the ball of cells becomesthe coelom. Blastula Gastrulation Gastrula with blastoporeDeuterostome – An animal in which the blastopore forms the anus and the mouth isformed later.Protostome – An animal in the blastopore form the mouth and the anus is formed later.Pseudocoelom – Some animals have a body cavity that forms in a different way. Insteadof forming from the interior of the gastrula, it forms later, once different layers of tissuehave formed.Organ Systems – Animals have evolved a series of specialized structures to performspecific functions. These structures are called organs. Organs are organized into organsystems. The major organ systems of animals are: nervous system, respiratory system,circulatory system, digestive system, excretory system, muscular, skeletal, andreproductive systems.Segementation – Many animals are segmented. Their bodies are divided into a series ofdistinct sections. An earthworm is an obvious and familiar example.Lophophore –The lophophore is a specialized feeding structure (a ring of ciliasurrounding the mouth) found in a few minor phyla including the Bryozoa. Thelophophore is used in fllter feeding.Animal Ways of Life.Habitats – Animals live in all major habitats in earth, in the ocean, fresh water, in the soil,on land, and inside other organisms (parasites).Feeding – Animals feed in a variety of ways. Herbivores eat plant material andcarnivores eat animal material. This can include solid food but also liquid food as well asmany animals feed on the body fluids of plants and or animals. An important way of lifefor many marine animals is filter feeding. Many animals filter small organisms andpieces of organic material from the water that passes over their bodies. Other animals areparasites and live inside of other organisms. They generally have greatly reduceddigestive systems.Reproduction and Development – Most